In many applications, for example in light ballast circuits having inductive loads, it may be necessary to switch the power transistor on and off when the load is operating with either positive and negative voltages. With common bipolar switches, i.e. NPN transistors, negative voltage spikes cause parasitic injection to the substrate. Therefore, common bipolar switches cannot be switched off when there is negative voltage on the load.
It is therefore an object of the present invention to provide a power switching circuit which overcomes, or at least reduces, the problems of known bipolar switches.